As the demand for integrated circuits having ever-smaller device features continues to increase, the need for improved illumination sources used for inspection of these ever-shrinking devices continues to grow. One such illumination source includes a laser-sustained plasma (LSP) source. Laser-sustained plasma light sources are capable of producing high-power broadband light. Laser-sustained plasma light sources operate by focusing laser radiation into a gas volume in order to excite the gas, such as argon, xenon, neon, nitrogen or mixtures thereof, into a plasma state, which is capable of emitting light. This effect is typically referred to as “pumping” the plasma.
The stability of plasma formed within an LSP light source is partially dependent on gas flows within the chamber housing the plasma. Unpredictable gas flows may introduce one or more variables which may hamper the stability of the LSP light source. By way of example, unpredictable gas flows may distort the plasma profile, distort the optical transmission properties of the LSP light source, and result in uncertainty regarding the position of the plasma itself. Previous approaches used to address unstable gas flows have been unable to achieve sufficiently high gas flow rates to sustain a predictable gas flow. Furthermore, those approaches which are capable of sustaining high gas flow rates introduce unwanted noise, require cumbersome, expensive equipment, and require additional safety management procedures.
Therefore, it would be desirable to provide a system and method that cure one or more shortfalls of the previous approaches identified above.